It is generally known to employ automated detectors which are responsive to images with high reflective contrast in the visible region of the spectrum for the machine processing of various types of information-bearing tickets, tags, labels, postage indicia and similar security markings. It is further known to employ automated detectors that are responsive to fluorescent emissions of security markings resulting from excitation at a shorter wavelength such as ultraviolet (UV) excitation. For example, in the postage meter art, mail pieces carrying postage indicia printed with fluorescent ink enhance the machine processing of the mail. In the United States and Canada, automatic equipment correctly faces or orients individual mail pieces by detecting red-fluorescence of postal indicia attached to mail pieces. Postal Service facing equipment employs a simple detector to locate the fluorescence. This detector does not verify that the fluorescence and the indicium image are physically coincident, thus limiting the ability of the detector to verify the authenticity of the security marking. As used herein, the term red-fluorescence refers not to the visible color of the ink but to fluorescence in the red region of the spectrum.
“Fluorescent security marking”, as used herein, refers to a security marking that fluoresces in a defined region of the spectrum upon exposure to a shorter wavelength excitation light such as UV light. The shift in wavelength between the incident excitation light and the fluorescent emission clearly distinguishes fluorescence from direct reflection. Fluorescent security markings are effectively applied to the detection of forged tickets, securities, identification cards, security papers, and the like. The difficulty of copying the fluorescence of security markings deters copying and provides forensic evidence of counterfeits. Among the applications of these security markings are the detection of articles, production marking, and automatic article identification. Intensity of the fluorescence is important to the success of these applications.
A counterfeiter without access to a printer with machine-readable fluorescent ink can produce a security mark that fluoresces and is machine-readable by printing the copied indicium over a fluorescent background, or by applying a fluorescent material over the copied indicium. In either case, the original and copied indicia are distinguishable. A forensic verifier system will make this distinction as described herein.
A manual forensic detection system can be simply a visible light source and an ultraviolet source with a switch that can switch between the two sources. An operator can view the indicium under the two light sources and verify the fluorescence of the image and the non-fluorescence of the background under ultraviolet illumination.
When an original security marking is illuminated with visible light, the image is dark against the bright background of the paper. When the original security marking image is illuminated with the ultraviolet light source, the image is bright against the low fluorescence background of the paper. Similarly, a copied security marking illuminated with visible light appears dark against a light background. Contrary to the properties of an image of an original security marking under ultraviolet illumination, a copied security marking printed on a fluorescent background or overprinted with fluorescent material and illuminated with ultraviolet light will show a dark image against the bright fluorescent background.
Rotary and other letterpress postage meters imprint the indicium on an envelope with a platen using an ink impregnated into a foam or other porous media. Red-fluorescent colored inks for letterpress meters include red, blue, green and black inks. For example, U.S. Pat. Nos. 2,681,317; 2,763,785; 3,230,221; 3,560,238; 3,928,226 and 4,015,131 disclose red-fluorescent inks for this purpose. These inks, in general, have a non-aqueous solvent-based vehicle system with a low vapor pressure, and have a high solid concentration, high viscosity, high boiling temperature and low surface tension. Letterpress technology lacks the ability of digital printing to print variable information. These letterpress inks therefore cannot be used in inkjet printers, which require stable solutions or stable dispersions with small particles, low viscosity and a specified surface tension. The viscosity of the liquid inks can vary from about 1.5 to 15 centipoise (cps) in current piezoelectric inkjet printers and from about 1 to 5 cps in thermal inkjet printers. The desirable surface tension of inkjet printer inks is between 30 to 50 dynes/cm. Examples of such red-colored, aqueous red-fluorescent inks are disclosed in U.S. Pat. No. 5,681,381. The disclosed inks fulfill USPS requirements for franking while being compatible with use in an inkjet printer. These inks are stable for extended periods of time. The formulations of these inks are based on water, co-solvent and penetrant solutions of water-soluble fluorescent toners. These inks are designed to achieve the required fluorescence intensity by limiting optical absorption, resulting in an optical density lower than that normally required for machine readability.
Postage indicia and franking machines have been developed to make use of digital printing and especially inkjet printing. An example is the Personal Post™ Postage Meter, which is manufactured by Pitney Bowes Inc. of Stamford, Conn. It is known in the art to print red colored, red-fluorescent indicia with variable data using digital printers. Digitally printed indicia provide significant advantages over letterpress indicia. Inkjet printing provides a means of printing indicia with high-density variable information. Pitney Bowes' PostPerfect meter produces a red-colored, red-fluorescent indicium with variable data by thermal transfer printing, while Personal Post Office produces red-colored, red-fluorescent indicia by inkjet printing. The USPS IBIP program allows the use of a black, machine-readable indicia. The Post Office equipment typically orients mail pieces bearing IBIP indicia using a facing identification mark or by a fluorescent tag added to the indicium. Postal services employ the machine-readable variable information for value added services, for cryptographic authentication of the indicium and for obtaining marketing information. Compared to letterpress technology, digital printers can provide print quality and contrast that does not decrease with the number of prints. The images can be printed at high resolution, high quality and at high speeds by direct, non-impact print engines. These inks have additional advantages for security markings since they may include penetrating solvents that cause the selective penetration of fluorescent component into the paper. This selective penetration provides rubbing and scratch resistance to the fluorescent component of the security markings.
Another problem is that the use of inkjet printing for postage franking is presently restricted, to some extent, by the lack of inks functional with inkjet technology that are simultaneously suitable for franking and machine-readability.
Postal services employ the information printed in the indicium for security and marketing purposes, as well as for processing the mail. In particular, the Information-Based Indicia Program (IBIP) of the USPS contains high-density, variable, cryptographically protected information in a two-dimensional bar code. To capture this information, postal scanning equipment must efficiently detect and read the information-based indicium. Postal indicia printed on various substrates have to display sufficient contrast in reflection to enable machine-readability. For example on dark substrates, such as Kraft envelopes with reflectance between 0.45 and 0.6, it is very difficult to achieve the desired contrast with red inks. Therefore, there is a strong need for printing security markings which exhibit high contrast, preferably black, and simultaneously red-fluorescence. However, red-fluorescent inks usually do not have enough contrast to be reliably read by optical character recognition (OCR) equipment, bar code readers and other types of machine vision technology. These systems often have illumination and detection systems in the red region of the spectrum.
A drawback of fluorescent security features is that there are a large variety of commercially available organic luminescent compounds. Common examples are the optical brighteners and commercially available colored-fluorescent materials and inks. Fraudulent replication of indicia would only demand substitution of the authentic material with a luminescent substance that emits light of a similar color. Thus, it is advantageous to provide luminescent inks with unique optical properties that cannot be simulated with materials that are easily available. The present invention provides inks with such unique optical properties.
Furthermore, in the mailpiece security system based on digital indicia, if the postage indicium is duplicated and produced on more than one mailpiece, it is very difficult for the Postal Service to tell which, among the mailpieces having identical indicium, has the original indicium.
Thus, it is advantageous and desirable to provide a method and a system to provide added security to the mailpiece, which can then be used to distinguish between mailpiece(s) that are legitimately paid for and those that are not.